Abstract

Background

The calsarcins comprise a novel family of muscle-specific calcineurin-interaction
proteins that play an important role in modulating both the function and substrate
specificity of calcineurin in muscle cells. The expression of calsarcin-1 (CS-1) is
restricted to slow-twitch skeletal muscle fibres, whereas that of both calsarcin-2
(CS-2) and calsarcin-3 (CS-3) is enriched in fast-twitch fibres. However, the transcriptional
control of this selective expression has not been previously elucidated.

Results

Our real-time RT-PCR analyses suggest that the expression of CS-1 and CS-2 is increased during the myogenic differentiation of mouse C2C12 cells. Promoter deletion
analysis further suggests that an NF-κB binding site within the CS-1 promoter is responsible for the up-regulation of CS-1 transcription, but no similar mechanism was evident for CS-2. These findings are further supported by the results of EMSA analysis, as well as
by overexpression and inhibition experiments in which NF-κB function was blocked by
treatment with its inhibitor, PDTC. In addition, the overexpression of NFATc4 induces
both the CS-1 and CS-2 promoters, whereas MEF2C only activates CS-1.

Conclusion

Our present data suggest that NF-κB is required for the transcription of mouse CS-1 but not CS-2, and that the regulation of the calsarcins is mediated also by the NFAT and MEF2
transcription factors. These results provide new insights into the molecular mechanisms
governing transcription in specific muscle fibre cells. The calsarcins may also serve
as a valuable mechanistic tool to better understand the regulation of calcineurin
signalling during muscle differentiation.